drm/imx: Remove of_node assignment from ipuv3-crtc driver probe

The crtc child device driver shouldn't modify the of_node of its platform
device in the probe function. Instead, since the previous patch, the IPU
core driver sets the of_node when the platform device is created.

Drop the now unused custom imx_drm_get_port_by_id function.

Suggested-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>